Optical coherence tomography (OCT) derives subsurface scattering information—amplitude, and/or phase, typically by temporal gating, or else by information obtained in the spectral domain, either by slewing the wavelength of a narrowband beam, or by dispersion of a broadband beam. OCT has manifold applications in many medical fields including ophthalmology, cardiology, oncology, otolaryngology, gastroenterology and dentistry, as well as in many non-medical applications such as materials imaging, non-destructive testing, quality control and coating measurements.
The use of a spatial interferogram to derive depth information, where the interferogram is created by interfering the scatter return from a sample with a reference beam derived from the illuminating source, has been described, for example, by Hauger et al., “Interferometer for Optical Coherence Tomography,” Appl. Opt., vol. 42, pp. 3896-3902 (2003), (hereinafter, “Hauger (2003)”) incorporated herein by reference. Hauger teaches a scatter return and a reference beam both coupled onto a linear CCD array via offset monomode optical fibers. The concept described by Hauger constitutes a particular instance of “Linear OCT.” Hauger shows the proportionality of the signal-to-noise ratio (SNR) in Linear OCT to the same variables as those limiting SNR in time-domain OCT, assuming shot-noise-limited detection. Linear optical coherence tomography was first described by Hauger et al., “High speed low coherence interferometer for optical coherence tomography,” SPIE Proc. 4619, pp. 1-9 (2002), and by Umetsu et al., “Non-scanning optical coherence tomography by an angular dispersion imaging method,” Opt. Rev., vol. 9, pp. 70-74 (2002), both of which publications are incorporated herein by reference. Generally stated, a relative tilt introduced between the sample and reference beams creates interference fringes along one direction. Encoded in these fringes is the relative time-of-flight of photons between the sample and reference arms. This results in a pseudo time-domain OCT (TD-OCT) system, but with the advantage of no moving components. Umetsu, however, provides a grating for angular-dispersion demodulation of the interference pattern created by the tilt between sample and reference beams, constraining the applicability of such a technique to particular geometries.
OCT has typically required an OCT system 100, of which an example is shown in FIG. 1, sized at least on the scale of a desktop computer, and coupled to an optical probe by optical fibers, or otherwise. More recent advances have used optical fibers to couple compact portable instruments to a core imaging unit, as described, for example in Shelton et al., “Optical coherence tomography for advanced screening in the primary care office,” J. Biophotonics, DOI: 10.1002/jbio.201200243, (Apr. 18, 2013), hereinafter, “Shelton (2013),” and in U.S. Pat. No. 8,115,934 (to Boppart, “Boppart '934”), both of which are incorporated herein by reference. FIGS. 2A and 2B (FIGS. 4C and 4D in Shelton (2013)), show images of a tympanic membrane TM with an accompanying biofilm 200 derived from a patient with chronic otitis media with instrumentation as that described in the Boppart '934 patent.
Various applications would benefit from the availability of a three-dimensional (3-D) imaging capability that is readily hand-held and self-contained, and there is, therefore, a clear need for leveraging the resources of a mobile device, such as a smart phone, to achieve the benefits of 3-D imaging.